1. Field of the Invention
The present invention relates to a liquid discharging head for discharging a desired liquid by generation of bubble with application of thermal energy to the liquid, and to a head cartridge and a liquid discharging device incorporating the liquid discharging head. More particularly, the present invention relates to a liquid discharging head having movable members arranged to be displaced by utilizing generation of bubble, and to a head cartridge and a liquid discharging device incorporating the liquid discharging head.
The present invention is the invention applicable to equipment such as a printer, a copying machine, a facsimile machine having a communication system, a word processor having a printer portion or the like, and an industrial recording device combined with one or more of various processing devices, with which recording is effected on a recording medium such as paper, thread, fiber, textile, leather, metal, plastic material, glass, wood, ceramic material, and so on.
It is noted here that "recording" in the present invention means not only provision of an image having meaning, such as characters or graphics, on a recorded medium, but also provision of an image having no meaning, such as patterns, on the medium.
2. Related Background Art
One of the conventionally known recording methods is an ink jet recording method for imparting energy of heat or the like to ink so as to cause a state change accompanied by a quick volume change of ink (generation of bubble), thereby discharging the ink through a discharge opening by acting force based on this state change, and depositing the ink on a recorded medium, thereby forming an image, which is so called as a bubble jet recording method. A recording apparatus using this bubble jet recording method is normally provided, as disclosed in the bulletin of U.S. Pat. No. 4,723,129 etc., with discharge openings for discharging the ink, ink flow paths in communication with the respective discharge openings, and electrothermal transducers as energy generating means for discharging the ink located in the ink flow path.
The above recording method permits high-quality images to be recorded at high speed and with low noise and in addition, because a head for carrying out this recording method can have the discharge openings for discharging the ink as disposed in high density, it has many advantages; for example, high-resolution recorded images or even color images can be obtained readily by compact apparatus. Therefore, this bubble jet recording method is used in many office devices including printers, copiers, facsimile machines, and so on in recent years and further is becoming to be used for industrial systems such as textile printing apparatus.
With spread of use of the bubble jet technology in products in wide fields, a variety of demands described below are increasing these years.
For example, an example of investigation to meet the demand to improve the energy use efficiency is optimization of the heat generating member such as adjustment of the thickness of a protecting film. This technique is effective to an improvement in transfer efficiency of generated heat into the liquid.
In order to provide high-quality images, proposed were driving conditions for realizing the liquid discharge method or the like capable of performing good ink discharge based on high-speed discharge of ink and stable generation of bubble. From the standpoint of high-speed recording, proposed was an improvement in a configuration of flow path in order to obtain a liquid discharging head with high filling (refilling) speed into the liquid flow path of the liquid discharged.
Among this configuration of liquid path, Japanese Patent Application Laid-open No. 63-199972, for example, describes the flow path structure as shown in FIGS. 38A and 38B. The flow path structure and the head producing method described in the application are of the invention accomplished noting the back wave occurring with generation of bubble (i.e., the pressure directed in the opposite direction to the direction toward the discharge opening, which is the pressure directed to a liquid chamber 1012). This back wave is known as loss energy, because it is not energy directed in the discharge direction.
The invention shown in FIGS. 38A and 38B discloses a valve 1010 located apart from a generation region of a bubble formed by a heat generating element 1002 and on the opposite side to the discharge opening 1011 with respect to the heat generating element 1002.
In FIG. 38B, this valve 1010 is illustrated as being produced by the producing method making use of a plate material or the like, having an initial position where it is stuck to the ceiling of the flow path 1003, and dropping into the flow path 1003 with generation of bubble. This invention is disclosed as the one for suppressing the energy losses by controlling a part of the aforementioned back wave by the valve 1010.
However, as apparent from investigation on the case where a bubble is generated inside the flow path 1003 as retaining the liquid to be discharged in this structure, it is seen that to regulate the part of the back wave by the valve 1010 is not practical for discharge of liquid.
The back wave itself originally has no direct relation with discharge, as discussed previously. At the point when the back wave appears in the flow path 1003, as shown in FIG. 38B, the pressure directly related to discharge out of the bubble is already ready to discharge the liquid from the flow path 1003. It is thus clear that to regulate the back wave, more accurately, to regulate the part thereof, cannot give a great effect on discharge.
In the bubble jet recording method, on the other hand, heating is repeated while the heat generating member is in contact with the ink, which forms deposits due to scorching of ink on the surface of the heat generating member. A large amount of the deposits could be formed depending upon the type of ink, which could result in unstable generation of bubble and which could make it difficult to discharge the ink in good order. It has been desired to achieve a method for well discharging the liquid without changing the property of the liquid to be discharged even if the liquid to be discharged is the one easily deteriorated by heat or even if the liquid is the one not easy to achieve adequate generation of bubble.
From this viewpoint, another proposal was made to provide a method to employ different types of liquids, a liquid (bubble generation liquid) for generating a bubble by heat and a liquid (discharge liquid) to be discharged, arranged to transmit the pressure upon generation of bubble to the discharge liquid and to discharge the discharge liquid thereby, for example as disclosed in Japanese Patent Application Laid-open No. 61-69467 and No. 55-81172, U.S. Pat. No. 4,480,259, and so on. In these publications, the ink as the discharge liquid is perfectly separated from the bubble generation liquid by a flexible film of silicone rubber or the like so as to keep the discharge liquid from directly contacting the heat generating member, and the pressure upon generation of bubble in the bubble generation liquid is transferred to the discharge liquid through deformation of the flexible film. By this structure, the method achieved prevention of the deposits on the surface of the heat generating member, an improvement in freedom of selection of the discharge liquid, and so on.
In the case of the head having the valve mechanism for preventing the back wave upon formation of bubble as in the conventional example shown in FIGS. 38A and 38B, however, while the discharge efficiency of liquid can be increased by the degree of prevention of the back wave transmitted to the upstream side, this structure prevents only escape of upstream-escaping components of the discharge force generated upon generation of bubble to the utmost, so that it is not always sufficient to achieve still larger increases of the discharge efficiency and the discharge force.
Further, in the case of the head of the structure in which the discharge liquid and the bubble generation liquid are completely separated from each other as described above, since the pressure upon bubble generation is transferred to the discharge liquid through the expansion/contraction deformation of the flexible film, the pressure by generation of bubble is absorbed to a quite high degree by the flexible film. In addition, since the deformation of the flexible film is not so large, the energy use efficiency and the discharge force could be degraded, though it is possible to achieve the effect by the separation of the discharge liquid from the bubble generation liquid.
As described above, spread of the bubble jet technology is under way in various fields these years, with which demands are increasing for a liquid discharging head etc. capable of broadening the freedom of selection as to the characteristics of discharge liquid including viscosity and thermal properties and capable of performing good discharge.
Returning to the principle of discharge of liquid droplet, some of the inventors thus have conducted extensive and intensive research to provide a novel liquid discharging method utilizing a bubble that has never been obtained heretofore, and a head used therein, and the like.
As a result, we established the utterly novel technology for positively controlling the bubble by arranging the fulcrum and free end of the movable member in the flow path in such a positional relation that the free end is located on the discharge opening side, that is, on the downstream side and by so arranging the movable member as to face the heat generating member or the bubble generation region.
Next, it was found that, considering the energy given to the discharge liquid by the bubble itself, a maximum factor to considerably improve the discharge properties was to take account of downstream growing components of the bubble. Namely, it was also clarified that the discharge efficiency and discharge rate were improved just by efficiently directing the downstream growing components of the bubble along the discharge direction. This led the present inventors to an extremely high technical level, as compared with the conventional technical level, that the downstream growing components of the bubble are positively moved to the free end side of the movable member.
Further, it was found that it was also preferred to take account of the structural elements such as the movable member, the liquid flow path, and so on related to the growth of bubble on the downstream side in the heating region for forming the bubble, for example, on the downstream side of the center line passing the center of the area of the electrothermal transducer in the direction of flow of liquid or on the downstream side of the center of the area of the surface contributing to the bubble generation.
It was further found that the refilling rate was able to be greatly improved taking account of the location of the movable member and the structure of the liquid supply paths.